Earthquakes are the most lethal of all natural disasters. What causes them?Geologists explain them in terms of a theory known as plate tectonics. Continentsare floating apart from each other; this is referred to as the continental drift. Aboutsixty miles below the surface of the sea, there is a semimolten bed of rock overwhich plates, or slabs, carry continents and sea floors at a rate of several inchesa year. As the plates separate from each other, a new sea floor is formed by themolten matter that was formerly beneath. Volcanic islands and large mountainranges are created by this type of movement. The collision of plates causesgeological instability such as that in California called the San Andreas Fault,located between the Pacific and North American plates. The plates there areconstantly pushing and pulling adjacent plates, thereby creating constant tremorsand a potential for earthquakes in the area
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